Process for the production of



United States l atent O PROCESS FOR THE PRODUCTION OF UNSATURATED KETONES Richard Norman Lacey, Hull, England, assignor to The Distillers Company Limited, Edinburgh, Scotland, 2! British company No Drawing. Application February 4, 1952, Serial No. 269,887

Claims priority, application Great Britain February 23, 195 1 11 Claims. (Cl. 260-5953 This invention relates to a method of producing unsaturated ketones.

The conventional method of producing allylacetone is by the alkylation of ethyl acetoacetate by means of metallic sodium and allyl chloride, followed by alkaline hydrolysis. Yields for this reaction are reported to be in the region of 45%-48% on the allyl chloride. The hydrolysis is, however, lengthy and the use of metallic sodium is undesirable on a large scale.

Allylacetone has also been obtained by refluxing a mixture of allyl acetoacetate and diphenyl ether, the latter acting as a high boiling diluent. A 31% yield only of allyl acetone was obtained after refluxing at 185200 C. for 92 hours.

The object of the present invention is to produce unsaturated ketones by a continuous process which does not suffer from the disadvantages of the prior art as indicated above, but which gives comparable or superior yields.

According to the present invention the process for the production of unsaturated ketones comprises pyrolysing esters of the general formula where the substituents R R R and R are hydrogen atoms or lower alkyl groups, in the vapour phase at temperatures between 300 and 600 C. The resulting reaction is indicated in general terms by:

By lower alkyl groups are meant alkyl groups of less than five carbon atoms, for instance, methyl, ethyl, isopropyl and n-bu-tyl groups. Thus the process of the invention is applicable to the pyrolysis of allyl acetoacetate and lower alkyl substituted allyl acetoacetates, for example the acetoacetates of: methallyl alcohol, crotyl alcohol, methyl vinyl carbinol (but-1-en-3-ol), pent-l-en-3-ol, hex-2-en-4-ol, Z-methylpent-Z-en-l-ol and 3-methylpent- 2-en-4-ol. The process is also applicable to the esters of the above alcohols with certain substituted acetoacetic acids, for example allyl propionoacetate. However, the preferred compounds are the acetoacetates of allyl alcohol and its lower homologues, in particular, the acetoacetates of allyl alcohol, crotyl alcohol and methallyl alcohol. The process may be carried out by vapourising the ester and passing the vapour through a tube heated to a temperature of between 300 and 600 C. It may also be carried out at superor sub-atmospheric pressures. The contact time of the ester with theheated zone may be adjusted by altering the feed rate or by adjusting the length or the heated zone. Generally times of from 0.5 to 15 2,766,289 Patented Oct. 9, 1956 seconds are suitable, depending on the temperature and the particular ester undergoing pyrolysis. Preferred tem-- peratures are from 450 to 550 C., although somewhat lower temperatures may be desirable for the esters of secondary alcohols which, although they rearrange to the ketone more readily than does the simple allyl acetoacetate; also give rise more readily to side reactions.

The esters may be prepared by ester exchange between the alkenol and a suitable alkyl acetoacetate or substituted acetoacetate. It has been found that this ester exchange can be carried out in conjunction with the pyrolysis by feeding the mixture directly to the pyrolysis zone. A very convenient method of preparing the acetoacetates is by the reaction of diketene with the alkenol in the presence of an alkaline catalyst, preferably a tertiary amine such as triethylamine. It has been found that the reaction mixture resulting from the interaction of diketene and the alkenol in the presence of triethylamine can be fed directly to the pyrolysing zone without the necessity for isolating the ester.

In a preferred embodiment of the invention, the ester is pyrolysed in the presence in the pyrolysing zone of the corresponding alkenol. This may be achieved very simply by using a stoichiometrical excess of the alkenol over the alkyl acetoacetate or the diketene used for preparing the ester, and then feeding the reaction mixture to the pyrolysing zone as indicated above. The proportion of alkenol to ester is not critical. With allyl acetoacetate, weight ratios of 0.522, 1:2 or even more may be used with success.

The pyrolysis products usually include some unchanged ester as well as the unsaturated ketone, carbon dioxide, and other products. Any unchanged ester, together with the alkenol if present may be recycled. The ketone may be isolated by distillation of the liquid pyrolysis product.

The following examples illustrate how the invention may be carried out in practice.

Example 1 In this example the pyrolysing zone consisted of a Pyrex (registered trademark) tube of 17 mm. bore heated by a furnace over 30 cm. of its length, and the allyl acetoacetate Was made from diketene and allyl alcohol.

250 grams of diketene (95% by weight) were added over 0.5 hour to 364 grams of allyl alcohol at 60 C. containing 0.1 gram of triethylamine, and the mixture was heated at 60 C. for a further 0.5 hour.

The product of this reaction, containing allyl acetoace tate, CH3.CO.CH2.CO.O.CH2.CH=CH2, and allyl alcohol, was fed at the rate of -l00 cc/hour to the pyrolysing zone and pyrolysed at 485-495 C., 520 grams of condensate being obtained in addition to 42.2 litres of a gas which was shown by analysis to contain 84% by volume of carbon dioxide. Distillation of the condensate gave, in addition to some low boiling material, 212.7 grams of allyl alcohol, 118.6 grams of allylacetone, CHa.CO.CH2.CH2.CH=CH2, 98.6 grams of allyl acetoacetate and 45.9 grams of high boiling residue Which was substantially dehydroacetic acid. Allowing for the allyl acetoacetate, which could usefully be recycled this corresponded to a yield of allylacetone of 63.7% by weight on allyl alcohol consumed, or 56.8% by weight on diketene consumed.

Further runs were carried out using the same pyrolysing apparatus. The table below shows the results obtained by varying (a) the ratio of allyl acetoacetate to allyl alco- 3 to hol in the feed, (12) the pyrolysis temperature and (c) the feed rate.

1 Feed wt. ratio: wt. allyl acetoacetate: wt. allyl alcohol. 9 With 10-11 litres/hr. nitrogen.

Runs 2 and 10 were carried out without the admixture of allyl alcohol with the ester; thus the feed wt. ratio is enumerated as 2:0. Run 10 shows that the allyl alcohol does not improve the yield of ketone merely by diluting the mixture, since the improved results of e. g. runs 4 and are not shown if nitrogen is substituted for the allyl alcohol vapour.

ExampleZ Example 3 To a mixture of methallyl alcohol (96 grams) and triethylamine (0.5 cc.) at 60-70 was added diketene (79 grams, 97%) over half an hour. When the addition was complete the product was heated for a further half hour.

The product methallyl acetoacetate was then fed at 80-90 cc./hr. through a Pyrex (registered r trademark) tube 17 mm. diameter, heated at 470-485 C. for 30 cm. of its length, giving 16.1 litres of gas (92% CO2) and 144.0 grams liquid product. Distillation of this product afforded 40.3 grams methallyl alcohol, 54.2 grams methallylacetone CH3.CO.CH2.CH2.C(CH3)=CH2 and 13.6 grams methallyl acetoacetate. Crediting the amounts of methallyl alcohol and methallyl acetoacetate, this corresponds to a yield of methallylacetone of 70.5% on methallyl alcohol and 58.7% on diketene.

Example 4 Crotyl acetoacetate CH3.CO.CH2.CO.O.CH2.CH=CH.CH3

was prepared from crotyl alcohol (93.5 grams, 1.3 moles) and diketene (110 grams, 96% 1.26 moles) and triethylamine (0.5 cc.). The product thus obtained was fed through the furnace at 490-5l0 C. at 90 cc./hr. In addition to considerable low boiling products there was obtained 27.6 grams crotyl alcohol, 37.1 grams S-methylhex-l-en-S-one, CH3.CO.CH2.CH(CH3).CH=CH2, 5.7

grams crotyl acetoacetate, giving a yield of the unsaturated ketone of 27.0% on diketene and 37.6% on crotyl alcohol.

Example 5 grams methyl vinyl carbinyl acetoacetate CH3.CO.CH2.CO.O.CH(CH3) .CH=CH2 were fed to the pyrolysis furnace at 60-70 cc./hr. at 410-420 C. 11.5 litres of gas (96% CO2) were evolved and 150.1 grams liquid products were collected. Distillation afforded 18.1 grams low-boiling hydrocarbons, substantially butadiene; 12.3 grams methyl vinyl carbinol, 25.0 grams crotyl acetone CH3.CO.CH2.CH2.CH= -CH.CH3

48.1 grams methyl vinyl carbinyl acetoacetate, equivalent to a yield of 32.7% crotyl acetone on methyl vinyl carbinyl acetoacetate, allowing for the recovered methyl vinyl carbinol. I

I claim:

1. A process for the production of an unsaturated ketone which comprises pyrolysing an ester of the general formula CHzR .CO.CH2.CO.O.CHR .CR =CHR where the substituents R R R and R are each selected from the group consisting of a hydrogen atom and a lower alkyl group, in the vapour phase at temperatures between 300 and 600 C.

2. A continuous process for the production of an unsaturated ketone which comprises pyrolysing an ester of the general formula CHzRKCOCI-Iz.(10.0.CHRRCR CI-IR where the substituents R R R and R are each selected from the group consisting of a hydrogen atom and a lower alkyl group, in the vapour phase at temperatures between 300 and 600 C., and recycling any of the said ester in the pyrolysis product back to the pyrolysis zone.

3. A continuous process according to claim 2, wherein the ester is pyrolysed in the presence in the pyrolysis zone of the alkenol corresponding to the alcohol component of the ester.

4. A continuous process according to claim 2, wherein the reaction mixture resulting from the interaction of diketene and the allcenol CHR =CR .CHR .OH in the presence of a tertiary amine is fed directly to the pyrolysing zone.

5. A continuous process according to claim 2, wherein a mixture of the alkenol CHR =CR .CHR .OH and a lower alkyl acetoaceta-te capable of undergoing alcoholysis therewith is fed into the pyrolyzing zone.

6. A continuous process according to claim 2, wherein the vapour of the ester is subjected to temperatures between 300 and 600 C. for 0.5 to 15 seconds.

7. A continuous process for the production of allyl acetone which comprises pyrolysing allyl acetoacetate at 450 C., and recycling any unaltered allyl acetoacetate in the pyrolysis product back to the pyrolysis zone.

8. A continuous process for the production of allyl acetone which comprises pyrolysing allyl acetoacetate at 500 C. in the presence in the pyrolysis zone of allyl alcohol, and recycling any unaltered allyl acetoacetate in the pyrolysis product back to the pyrolysis zone.

9. A continuous process for the production of methallyl acetone which comprises pyrolysing methallyl acetoacetate at 470-485 C., and recycling any unaltered methallyl acetoacetate in the pyrolysis product back to the pyrolysis zone.

10. A continuous process for the production of 3-methylhex-l-en-S-one which comprises pyrolysing crotyl acetoacetate at 490-510 C., and recycling any unaltered crotyl acetoacetate in the pyrolysis product back to the pyrolysis zone.

11. A continuous process for the production of crotyl acetone which comprises pyrolysing methyl vinyl carbinyl acetoacetate at 410-420 C., and recycling any unaltered methyl vinyl carbinyl acetoacetate in the pyrolysis product 2,256,149 back to the pyrolysis zone. 2,63 8,484

References Cited in the file of this patent UNITED STATES PATENTS 5 934,377 2,225,542 Allen et a1 Dec. 17, 1940 646,962 2,251,983 Chitwood Aug. 12, 1941 6 Long Sept. 16, 1941 Kimel May 12, 1953 FOREIGN PATENTS France May 20, 1948 Great Britain Nov. 12, 1950 

1. A PROCESS FOR THE PRODUCTION OF AN UNSATURATED KETONE WHICH COMPRISES PYROLYSING AN ESTER OF THE GENERAL FORMULA 